The present invention relates to a method for sensing the crankshaft position on an internal combustion engine and more particularly on an engine having an induction type combined starter/alternator. This invention was made with Government support under Prime Contract No. DE-AC-36-83CH10093, Subcontract No. ZCB-4-13032-02, awarded by the Department of Energy. The Government has certain rights in this invention.
For environmental and other reasons generally, there is a desire to provide for automotive vehicles that operate with propulsion system other than just a typical internal combustion engine. One such propulsion system contemplated is a purely electric vehicle. But since the technology for purely electrical vehicles is not yet practical, (e.g., there are limitations not desired by consumers), combining the electric drive with a somewhat more conventional internal combustion engine is one alternative being considered. With two drive systems in the hybrid vehicle, however, both drive systems, including the internal combustion engine, must be minimal in size.
One of the developments for reducing the overall space taken by the internal combustion engine and its accessories is to substantially reduce in size or even to eliminate the flywheel that normally mounts to the crankshaft at the rear of the engine and to locate a combined starter/alternator in this position. This will substantially reduce the space taken by separate conventional starters and alternators. For instance, an electric machine rotor of the starter/alternator can double as the conventional flywheel.
However, this now creates an electromagnetic interference (EMI) rich environment at the rear of the engine within which the crankshaft position is preferably sensed for the hybrid vehicle. The new system now requires that the sensor operate in the presence of strong electromagnetic fields beneath end turns of a stator and alongside an induction machine rotor. Current production technology, such as Hall effect or Variable Reluctance sensors (VRS), for sensing crankshaft position, then, is unusable in a combined starter/alternator system due to the significant EMI, which is not present at these levels in a conventional flywheel configuration.
To overcome this, one could relocate current crankshaft position sensors to the front of the internal combustion engine, but then the desired resolution of the crankshaft position for this hybrid configuration would be lost. This resolution is needed to more accurately control an indirect field oriented induction machine, thus making relocation an inadequate solution. Consequently, there is a desire to allow for accurate crankshaft position sensing even in an EMI rich field created by an engine with a combined starter/alternator mounted at its rear.
In its embodiments, the present invention contemplates a method of determining a crankshaft position for a rotating crankshaft in an internal combustion engine having a combined starter/alternator and a camshaft. The method comprises the steps of: rotating the crankshaft; rotating a tone wheel with indications thereon at the same angular velocity as the crankshaft; sensing the indications on the tone wheel, from a first location, as they rotate; producing an initial crankshaft position signal; rotating the camshaft; sensing the rotational position of the camshaft; producing a camshaft rotational position signal; filtering the initial crankshaft position signal based upon the camshaft rotational position signal to produce a filtered crankshaft position signal; and gain limiting the filtered crankshaft position signal to produce a crankshaft rotational position signal.
Accordingly, an object of the present invention is to allow for a preferred location for crank position sensing at the rear of the engine when employing an induction type flywheel starter/alternator system.
A further object of the present invention is to allow for accurate signal determination by employing bandpass and tracking filters, for robust sensing in the EMI rich environment around the starter/alternator.
An advantage of the present invention is that a VRS or Hall Effect Sensor can accurately measure crankshaft position even when subjected to an EMI rich environment from a hybrid electric vehicle.